Radio-Frequency Identification (RFID) systems typically include RFID readers, also known as RFID reader/writers or RFID interrogators, and RFID tags. RFID systems can be used to inventory, locate, identify, authenticate, configure, enable/disable, and monitor items to which the tags are attached or in which the tags are embedded. RFID systems may be used in retail applications to inventory and track items; in consumer- and industrial-electronics applications to configure and monitor items; in security applications to prevent item loss or theft; in anticounterfeiting applications to ensure item authenticity; and in myriad other applications.
RFID systems operate by an RFID reader interrogating one or more tags using a Radio Frequency (RF) signal. The RF signal is typically electromagnetic, at least in the far field. The RF signal can also be predominantly electric or magnetic in the near field. The RF signal may encode one or more commands that instruct the tags to perform one or more actions.
A tag that senses the interrogating RF signal may reply with a responding RF signal (a response). The responding RF signal may be generated by the tag, or it may be formed by the tag reflecting back a portion of the interrogating RF signal in a process known as backscatter. Backscatter may take place in a number of ways.
The reader receives, demodulates, and decodes the response. The decoded response may include data stored in the tag such as a serial number, price, date, time, destination, encrypted message, electronic signature, other attribute(s), any combination of attributes, or any other suitable data. The decoded response may also encode status information about the tag, the item to which the tag is attached, or the item into which the tag is embedded such as a tag status message, item status message, configuration data, or any other status information.
An RFID tag typically includes an antenna and an RFID integrated circuit (IC) comprising a radio section, a power management section, and frequently a logical section, a memory, or both. In some RFID ICs the logical section includes a cryptographic algorithm which may rely on one or more passwords or keys stored in tag memory. In earlier RFID tags the power management section often used an energy storage device such as a battery. RFID tags with an energy storage device are known as battery-assisted, semi-active, or active tags. Advances in semiconductor technology have miniaturized the IC electronics so that an RFID tag can be powered solely by the RF signal it receives. Such RFID tags do not include a long-term energy-storage device and are called passive tags. Of course, even passive tags typically include temporary energy- and data/flag-storage elements such as capacitors or inductors.